3,245 research outputs found
Accretion and activity on the post-common-envelope binary RR~Cae
Current scenarios for the evolution of interacting close binaries - such as
cataclysmic variables (CVs) - rely mainly on our understanding of low-mass star
angular momentum loss (AML) mechanisms. The coupling of stellar wind with its
magnetic field, i.e., magnetic braking, is the most promising mechanism to
drive AML in these stars. There are basically two properties driving magnetic
braking: the stellar magnetic field and the stellar wind. Understanding the
mechanisms that drive AML therefore requires a comprehensive understanding of
these two properties. RRCae is a well-known nearby (d=20pc) eclipsing DA+M
binary with an orbital period of P=7.29h. The system harbors a metal-rich cool
white dwarf (WD) and a highly active M-dwarf locked in synchronous rotation.
The metallicity of the WD suggests that wind accretion is taking place, which
provides a good opportunity to obtain the mass-loss rate of the M-dwarf
component. We analyzed multi-epoch time-resolved high-resolution spectra of
RRCae in search for traces of magnetic activity and accretion. We selected a
number of well-known activity indicators and studied their short and long-term
behavior. Indirect-imaging tomographic techniques were also applied to provide
the surface brightness distribution of the magnetically active M-dwarf, and
reveals a polar feature similar to those observed in fast-rotating solar-type
stars. The blue part of the spectrum was modeled using a atmosphere model to
constrain the WD properties and its metal enrichment. The latter was used to
improve the determination of the mass-accretion rate from the M-dwarf wind. The
presence of metals in the WD spectrum suggests that this component arises from
accretion of the M-dwarf wind. A model fit to the WD gives Teff=(7260+/-250)K
and logg=(7.8+/-0.1) dex with a metallicity of =(-2.8+/-0.1)dex,
and a mass-accretion rate of dotMacc=(7+/-2)x1e-16Msun/yr.Comment: 14 pages, 7 Figures, 6 Table
Characterisation of Contemporary Slavery through the Analysis of Accommodation Conditions
Slave labour or work in conditions analogous to slavery continues on all continents and sometimes tends to be mistaken for simple violations of labour laws. Therefore, this work aims to identify parameters that allow distinguishing between situations of non-compliance with labour legislation and modern rural slavery in Brazil through the analysis of accommodation conditions. To achieve this objective, a bibliographic research was developed in six databases on sanitary, accommodation and clothing issues of enslaved workers in the 19th century in Brazil. The resulting data were compared with data from a sample of 392 proven cases of neoslavery detected between 2007 and 2017 in Brazil. The analysis focused on the general conditions of the physical structures necessary to protect workers against bad weather, animal attacks, violence, sanitary conditions to support physiological and asepsis needs, as well as the clothing provided and used. Similarities were found in the accommodation conditions between enslaved and neoenslaved workers in Brazil between the 19th and 21st centuries. The availability of sanitary conditions (toilets), rest (bedrooms/dormitories), and the general housing structure are very similar. Future research may point towards identifying other parameters and developing a tool to help authorities unequivocally identify neoslavery situations
Parameter space of experimental chaotic circuits with high-precision control parameters
ACKNOWLEDGMENTS The authors thank Professor Iberê Luiz Caldas for the suggestions and encouragement. The authors F.F.G.d.S., R.M.R., J.C.S., and H.A.A. acknowledge the Brazilian agency CNPq and state agencies FAPEMIG, FAPESP, and FAPESC, and M.S.B. also acknowledges the EPSRC Grant Ref. No. EP/I032606/1.Peer reviewedPublisher PD
Shear strength of adhesively bonded polyolefins with minimal surface preparation
Interest in polyethylene and polypropylene bonding has increased in the last years. However, adhesive joints with adherends which are of low surface energy and which are chemically inert present several difficulties. Generally, their high degree of chemical resistance to solvents and dissimilar solubility parameters limit the usefulness of solvent bonding as a viable assembly technique. One successful approach to adhesive bonding of these materials involves proper selection of surface pre-treatment prior to bonding. With the correct pre-treatment it is possible to glue these materials with one or more of several adhesives required by the applications involved. A second approach is the use of adhesives without surface pre-treatment, such as hot melts, high tack pressure-sensitive adhesives, solvent-based specialty adhesives and, more recently, structural acrylic adhesives as such 3M DP-8005® and Loctite 3030®.
In this paper, the shear strengths of two acrylic adhesives were evaluated using the lap shear test method ASTM D3163 and the block shear test method ASTM D4501. Two different industrial polyolefins (polyethylene and polypropylene) were used for adherends. However, the focus of this study was to measure the shear strength of polyethylene joints with acrylic adhesives. The effect of abrasion was also studied. Some test specimens were manually abraded using 180 and 320 grade abrasive paper. An additional goal of this work was to examine the effect of temperature and moisture on mechanical strength of adhesive joints
Physical activity level in Physical Therapy students
Physical activity is defined as any body movement that requests energy expenditure. The practice of physical activity allows to reinforce and increase the capacity of muscular-skeletal response and an improvement of physical aptitude. Currently, has been verified that university students have been decreasing healthy lifestyles and increasing their degree of sedentary lifestyle. Thus, it’s essential the Higher Education Institutions present themselves as a way to promote the practice of physical activity and contemplating it in the basic formation.info:eu-repo/semantics/publishedVersio
Dynamical estimates of chaotic systems from Poincar\'e recurrences
We show that the probability distribution function that best fits the
distribution of return times between two consecutive visits of a chaotic
trajectory to finite size regions in phase space deviates from the exponential
statistics by a small power-law term, a term that represents the deterministic
manifestation of the dynamics, which can be easily experimentally detected and
theoretically estimated. We also provide simpler and faster ways to calculate
the positive Lyapunov exponents and the short-term correlation function by
either realizing observations of higher probable returns or by calculating the
eigenvalues of only one very especial unstable periodic orbit of low-period.
Finally, we discuss how our approaches can be used to treat data coming from
complex systems.Comment: subm. for publication. Accepted fpr publication in Chao
Level of physical activity and body image in Portuguese and French students, 1st year of Physiotherapy
Adolescents have a physiological need to move, therefore physical activity should be encouraged at an early age. In young adults, there are also various physical and psychological transformations. Associated with these transformations, there is a will to fit in the patterns of society’s beauty and, sometimes, a consequent bodily dissatisfaction. Thus, it is necessary to encourage physical activity, for its benefits.info:eu-repo/semantics/publishedVersio
Cutting forces and wear analysis of Si3N4 diamond coated tools in high speed machining
Si3N4 tools were coated with a thin diamond film using a Hot-Filament Chemical Vapour Deposition (HFCVD) reactor, in order to machining a grey cast iron. Wear behaviour of these tools in high speed machining was the main subject of this work. Turning tests were performed with a combination of cutting speeds of 500, 700 and 900 m min−1, and feed rates of 0.1, 0.25 and 0.4 mm rot−1, remaining constant the depth of cut of 1 mm. In order to evaluate the tool behaviour during the turning tests, cutting forces were analyzed being verified a significant increase with feed rate. Diamond film removal occurred for the most severe set of cutting parameters. It was also observed the adhesion of iron and manganese from the workpiece to the tool. Tests were performed on a CNC lathe provided with a 3-axis dynamometer. Results were collected and registered by homemade software. Tool wear analysis was achieved by a Scanning Electron Microscope (SEM) provided with an X-ray Energy Dispersive Spectroscopy (EDS) system. Surface analysis was performed by a profilometer
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